All ships have a minimum of two wind transmitters,located on the port and starboard yardarms. The switchused to control the transmitter in use is usually locatedon the bridge on smaller ships, but may be located in thegeophysics office aboard aircraft carriers. Normally,the windward-side transmitter is used. The transmittersare very similar to the ML-400/UMQ-5 transmitters.The transmitter selected reports wind directionrelative to the bow of the ship and wind speed relative tothe ship’s motion. These winds are called relative winds.Several Type B-3 relative wind indicators (fig. 2-27) areinstalled throughout each ship in various locations. Toconvert relative wind to true wind, you must also knowthe ship’s true heading (available from the magneticcompass [fig. 2-28] or gyroscope repeater [fig. 2-29]),as well as the ship’s speed (available from theunderwater-speed log indicator [fig. 2-30]). If amagnetic compass is used for the ship’s course, to obtaina true heading, the magnetic declination must be addedto the compass heading before that number is used in atrue-wind computation. Gyro repeaters are preferablefor conversion, since these readings are true headings.Both gyro repeaters and underwater-speed logindicators are usually located in the geophysics office,as well as on the bridge and at other strategic locationsthroughout the ship.Figure 2-27.—Type B-3 shipboard relative-wind direction andrelative-wind speed indicator.Figure 2-28—Shipboard magnetic compass.Figure 2-29.—Shipboard pelorus with a gyroscope repeater.2-21
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